In humans, a number of inherited disorders occur in lysosomal sphingolipid catabolism (commonly known as “sphingolipidoses”). For example, an inherited deficiency of the lysosomal sphingomyelinase underlies Niemann-Pick disease, and defective activity of the lysosomal ceramidase causes Farber disease. The most frequently encountered disorder of sphingolipid catabolism is Gaucher disease (Barranger J A and Ginns E I.1989. Glucosylceramide lipidoses: Gaucher's disease. In: The Metabolic Basis of Inherited Diseases. C R Scriver, A L Beaudent, W S Sly & D Valle, Eds. McGraw-Hill Inc. New York, 1677-1698). The metabolic basis of this disorder is a deficiency in activity of the catabolic beta-glucosidase enzyme, glucocerebrosidase (E.C.3.2.1.45), which catalyzes the hydrolysis of glucosylceramide (glucocerebroside) to glucose and ceramide.
In patients with Gaucher disease glucosylceramide (GlcCer) accumulates in tubular aggregates, in particular in lysosomes of macrophages. The lipid-laden macrophages have a typical morphology and are usually referred to as “Gaucher cells”. In the course of clinical manifestation of Gaucher disease the abnormal macrophages may accumulate in large quantities in various body locations, such as the bone marrow compartment, spleen, liver, kidney, and lungs. The most pronounced clinical symptoms associated with Gaucher disease are progressive splenomegaly, hepatomegaly, and skeletal deterioration. Most Gaucher disease patients do not develop neurological complications. The common non-neuronopathic form of the disease is called Type 1 Gaucher disease. In very severe cases of Gaucher disease characteristic neurological abnormalities may also occur, resulting in lethal complications at infantile (Type 2) or juvenile (Type 3) stages of development.
In recent years, several therapies have been proposed for the treatment of Gaucher disease. Since 1990 an effective therapeutic intervention for Gaucher disease is available, based on the chronic supplementation of patients with human glucocerebrosidase (Barton N W Furbish F S Murray G J Garfield M Brady R O.1990. Therapeutic response to intravenous infusion of glucocerebrosidase in a patient with Gaucher disease. Proc Natl Acad Sci USA 87:1913-1916). Glucocerebrosidase isolated from human placenta (U.S. Pat. No. 3,910,822) was the first source for a commercial form of glucocerebrosidase replacement therapy (CEREDASE®, produced by Genzyme Corp.). Later commercial production for enzyme replacement therapy included CEREZYME®, a recombinant enzyme produced in CHO cells, also by Genzyme Corp. (U.S. Pat. Nos. 5,236,838; and 5,549,892). U.S. Pat. Nos. 5,879,680 and 6,074,684 disclose cloned DNA for synthesizing human glucocerebrosidase. Conjugates of the glucocerebrosidase enzyme with polyethylene glycol (PEG) have also been proposed by Enzon Inc. for treatment of Gaucher's disease (see for example U.S. Pat. Nos. 5,705,153 and 5,620,884).
The most pronounced beneficial effects of enzyme replacement therapy are the reduction in liver and spleen volumes, and the improvements in hematological parameters such as hemoglobulin concentration and thrombocyte and leukocyte counts. However, marked inter-individual differences exist in the rate and extent of clinical response, even among related patients that are treated with the same dosing regimen. In general, the most marked clinical improvements occur within the first year of treatment, accompanied by a pronounced correction of biochemical serum abnormalities. A complete reversal of clinical signs and complete normalization of serum abnormalities, such as elevated levels of angiotensin converting enzyme, tartrate-resistant acid phosphatase and chitotriosidase, is not achieved by enzyme therapy, not even in the case of patients that receive high doses of glucocerebrosidase for a number of years. In addition, the costs associated with successful enzyme replacement therapy have hitherto been exceptionally high, so that enzyme therapy of Gaucher disease is one of the most expensive drug treatments for any disease. Notably, although the glucocerebrosidase enzyme preparation is known to contain minor amounts of human chorionic gonadotropin (HCG) and other impurities, the experience so far indicates that enzyme therapy is safe.
Another approach for treatment of the disease is gene therapy. In general, pluripotent hematopoietic stem cells are isolated and transduced with a vector containing human glucocerebrosidase cDNA. The transduced cells are then transplated into a Gaucher disease patient to provide therapeutically effective levels of glucocerebrosidase activity. For example, U.S. Pat. No. 5,911,983 discloses methods for transplantation of hematopoietic stem cells comprising retroviral vectors which express the glucocerebrosidase gene into a Gaucher disease patient, to provide therapeutically effective levels of glucocerebrosidase activity. U.S. Pat. No. 6,066,626 discloses vectors comprising a transgene encoding a biologically active human lysosomal enzyme, wherein such vector enables sustain expression of the biologically active enzyme in mammalian cells.
An additional recent approach for the treatment of Gaucher disease is the so called “substrate deprivation therapy”. According to this approach a marked reduction in the synthesis of GlcCer may have a beneficial effect because the amount of GlcCer that has to be degraded by macrophages would be lower. Several inhibitors of GlcCer synthase have been developed, e.g. 1-phenyl-decanoylamino-3-morpholino-1-propanol (PDMP) and its analogue 1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol (PPMP) (Abe A Radin N S Shayman A. 1996. Induction of glucosylceramide synthase by synthase inhibitors and ceramide Biochim. Biophys. Acta 1299:333-341), butyl-deoxynojirimycin (Platt F M Neises G R Dwek R A Butters T D. 1994. N-butyldeoxynojirimycin is a novel inhibitor of glycolipid biosynthesis J Biol Chem 269:8362-8365) and butyl-deoxygalactonojirimycin (Platt F M Neises G R Karlsson G B Dwek R A Butters T D. 1994. N-butyldeoxygalactonojirimycin inhibits glycolipid biosynthesis but does not affect N-linked oligosaccharide processing. J Biol Chem 269:27108-27114; U.S. Pat. Nos. 5,472,969; 5,786,368; 5,798,366; and 5,801,185).
A disadvantage of the “substrate deprivation” approach is that a priori not only the synthesis of GIcCer but also that of more complex glycosphingolipids is inhibited. Moreover, the presently available inhibitors of GIcCer synthase are known to exert a number of important biological effects that may limit their applicability as therapeutic agent. For example, PDMP is known to induce apoptosis in some cell types. Butyl-deoxynojirimycin is known to inhibit also the lysosomal glucocerebrosidase and the α-glucosidase I, an ER enzyme that plays a critical role in trimming of N-linked glycans in newly formed glycoproteins, and as such in quality control of protein folding. The antiviral action of butyldeoxynojirimycin may be due to its inhibitory effect on glycoprotein modification. Moreover, it was recently reported that GlcCer synthase inhibitors induce the synthesis of the enzyme. Consequently, these inhibitors would need to be chronically administered to Gaucher patients since their withdrawal would be followed by an abnormally high level of GlcCer synthase activity and increased load of GlcCer.
U.S. Pat. No. 6,177,447 discloses the use of deoxynojirimycin derivatives as glucosylceramidase inhibitors, suggesting that glucosylceramidase activity stimulates activation of macrophages, and therefore specific inhibition of the enzyme activity would prevent further release of pathogenetic factors and disrupt the pathological cascade, resulting in therapeutic effect.
Still another treatment approach is the combination drug therapy, in which typically two of the above described therapies, for example, enzyme replacement and substrate deprivation therapy are combined (for example, U.S. patent application Ser. Nos. 2001/0,044,453; 2002/0,127,213; International Patent Application WO 00/62779).
Juvenile (Type 3) Gaucher patients were successfully treated by bone marrow transplantation. The introduction of the normal genetic information for glucocerebrosidase in hematopoietic stem cells results in the formation of blood cells able to hydrolyze GlcCer at normal rates. Unfortunately, the applicability of bone marrow transplantation as treatment for Gaucher disease is quite restricted due to the limited availability of bone marrow from matched donors and the considerable morbidity associated with this intervention, particularly in the case of adults.
In summary, all the above-described therapies attempt only to overcome the defective activity of the enzyme glucocerebrosidase. This is also true for other glycolipid storage diseases, wherein similar therapeutic approaches are undertaken to overcome the defective activity of the aberrant catabolic enzyme (for example, U.S. Pat. Nos. 6,465,488; 6,066,626; U.S. patent application Ser. No. 2002/0142985).
Thus, there is a recognized need for, and it would be highly advantageous to have alternative targets for novel drug therapies, wherein such therapies may be used alone or in conjunction with the existing treatments of glycolipid storage diseases.